Four-Cable Scissors Grab With Single-Pass Closing Sheaves
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Solution Overview
Problem
Scissors grabs are relatively expensive to construct compared to clamshell grabs, and existing designs with a maximum opening angle of 50-70 degrees may not optimize operational efficiency and construction simplicity.
Innovation Solution
A four cable operated scissors grab design with scissor levers featuring a hoist cable connection on one side and a closing cable connection on the opposite side, incorporating a single final closing sheave on each lever, and stiffening profiles for enhanced structural efficiency and reduced maintenance points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a traditional four cable operated scissors grab is used with multiple closing sheaves, then the grab can achieve sufficient closing force, but the construction becomes more complex and maintenance requirements increase
Solution Approach 1:
The patent extracts and eliminates unnecessary intermediate closing sheaves from the traditional four-sheave configuration, retaining only the essential first and final closing sheaves. This reduction from multiple sheaves to just two per lever maintains the necessary closing force while significantly simplifying the overall construction and reducing maintenance points.
Solution Approach 2:
The patent inverts the traditional cable routing arrangement by having the closing cable extend in a single pass from the closing cable connection on one lever, through the closing sheaves on the other lever, back to the closing cable connection on the first lever. This inverted single-pass configuration achieves the necessary mechanical advantage with fewer sheaves compared to the traditional multi-pass arrangement.
2Ease of operation
If the closing cable stroke is made long to achieve full opening and closing movement, then the grab can operate through the full range of motion, but the opening and closing times increase reducing operational efficiency
Solution Approach 1:
The patent optimizes the geometric parameters of the lever arms and the positioning of the closing cable connections to achieve a more favorable mechanical advantage ratio. This parameter optimization allows the closing cable to travel a shorter distance while still achieving the full 50-70 degree opening angle, thereby reducing opening and closing times without sacrificing range of motion.
3Quantity of substance
If the maximum opening angle is increased beyond 50-70 degrees, then the grab can handle larger volumes of material, but the structural stability and control precision deteriorate
Solution Approach 1:
The patent applies partial action by limiting the maximum opening angle to the optimal 50-70 degree range rather than allowing full 180 degree opening. This partial opening range is sufficient for effective bulk material handling while maintaining structural stability, control precision, and avoiding the harmful effects of excessive opening angles.
4Force
If multiple pivot connections are used in the scissor lever configuration, then the grab achieves the scissored mechanical advantage, but the number of maintenance points and construction cost increase
Solution Approach 1:
The patent merges the functions of multiple pivot connections into a simplified scissor lever arrangement with reduced pivot points. The scissor levers are configured to pivot about a common pivoting axis, combining multiple rotation points into a single efficient pivot mechanism that maintains the mechanical advantage while reducing the number of separate pivot connections requiring maintenance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design simplifies construction, reduces opening and closing times, and maintains operational efficiency with a limited maximum opening angle of 50-70 degrees, facilitating a lightweight and stiff structure.
Implementation Method 1
a pair of scissor levers that are connected via a pivot joint to pivot about a pivoting axis
Implementation Method 2
the scissor levers each include a sheave on the second side of the lever, wherein said sheaves are each arranged as a first and final closing sheave for the closing cable
Implementation Method 3
in use a dedicated hoisting cable is fastened to each lever on the first side of the lever, and a dedicated closing cable is fastened to each lever at the second side of the lever
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A four cable operated scissors grab (1), comprising a pair of scissor levers (2a, 2b) that are pivotably connected via a pivot joint (3), which scissor levers each include a grab shell (5a, 5b) and a hoist cable connection situated on a first side of the lever with respect to the pivot joint, and a closing cable connection (8a, 8b) situated on a second side of the lever that is opposite with respect to the pivot joint, so that in use a dedicated hoisting cable is fastened to each lever on the first side of the lever, and a dedicated closing cable is fastened to each lever at the second side of the lever, in which the scissor the levers are arranged to pivot about the pivot axis (4) between a closed position of the grab in which side and bottom edges of the shells are adjacent each other and the shells cooperate to form a bucket that can hold material to be handled, and a fully opened position of the grab in which the side and bottom edges are spaced apart and define a maximum opening there between through which material to be handled can pass, wherein when the grab moves from the closed position to the fully opened open position, a plane through the pivot axis and the side and bottom edges of each grab shell has an angular displacement about the pivot axis that is included in the range of 50 - 70 degrees.